Bug 1876415 - Make timestamp formats consistent between Jitdump and the marker file. r=glandium

On Linux and Android, both jitdump and the marker file will keep using
`CLOCK_MONOTONIC` nanoseconds, as before.

On macOS, both jitdump and the marker file will now be using
`TimeStamp::RawMachAbsoluteTimeNanoseconds()` , i.e. "nanoseconds since
mach_absolute_time origin".
This value has the advantage that it is also relatively easy to obtain
in other browser engines, because their internal timestamp value is stored
in milliseconds or nanoseconds rather than in `mach_absolute_time` ticks.
In the past, on macOS, Firefox was using `CLOCK_MONOTONIC` nanoseconds for
jitdump and `TimeStamp::RawMachAbsoluteTimeValue()` for the marker file.
This inconsistency is now fixed.
I will update samply to change how it treats jitdump timestamps on macOS.
There are no other consumers of jitdump files on macOS that I know of.

On Windows, we will keep using raw QPC values for the marker file - this
matches what's in the ETW events. Jitdump on Windows is mostly unused but
I'm updating it to match.

Furthermore, this fixes the order in mozglue/misc/moz.build to make sure
we always use the TimeStamp_darwin implementation on Darwin (and not just
due to a broken configure check, see bug 1681445), and it fixes the #ifdef
in TimeStamp.h to match the Darwin check.

Differential Revision: https://phabricator.services.mozilla.com/D199592

dom/performance/Performance.cpp

@@ -615,8 +615,8 @@ void Performance::MaybeEmitExternalProfilerMarker(
   uint64_t rawStart = startTimeStamp.RawQueryPerformanceCounterValue().value();
   uint64_t rawEnd = endTimeStamp.RawQueryPerformanceCounterValue().value();
 #elif XP_MACOSX
-  uint64_t rawStart = startTimeStamp.RawMachAbsoluteTimeValue();
-  uint64_t rawEnd = endTimeStamp.RawMachAbsoluteTimeValue();
+  uint64_t rawStart = startTimeStamp.RawMachAbsoluteTimeNanoseconds();
+  uint64_t rawEnd = endTimeStamp.RawMachAbsoluteTimeNanoseconds();
 #else
   uint64_t rawStart = 0;
   uint64_t rawEnd = 0;

js/src/jit/PerfSpewer.cpp

@@ -123,9 +123,16 @@ AutoLockPerfSpewer::~AutoLockPerfSpewer() { PerfMutex.unlock(); }
 
 #ifdef JS_ION_PERF
 static uint64_t GetMonotonicTimestamp() {
-  struct timespec ts = {};
-  clock_gettime(CLOCK_MONOTONIC, &ts);
-  return ts.tv_sec * 1000000000 + ts.tv_nsec;
+  using mozilla::TimeStamp;
+#  ifdef XP_LINUX
+  return TimeStamp::Now().RawClockMonotonicNanosecondsSinceBoot();
+#  elif XP_WIN
+  return TimeStamp::Now().RawQueryPerformanceCounterValue().value();
+#  elif XP_MACOSX
+  return TimeStamp::Now().RawMachAbsoluteTimeNanoseconds();
+#  else
+  MOZ_CRASH("no timestamp");
+#  endif
 }
 
 // values are from /usr/include/elf.h

mozglue/misc/TimeStamp.h

@@ -474,8 +474,9 @@ class TimeStamp {
   }
 #endif
 
-#ifdef XP_MACOSX
-  uint64_t RawMachAbsoluteTimeValue() { return static_cast<uint64_t>(mValue); }
+#ifdef XP_DARWIN
+  // Returns the number of nanoseconds since the mach_absolute_time origin.
+  MFBT_API uint64_t RawMachAbsoluteTimeNanoseconds() const;
 #endif
 
 #ifdef XP_WIN

mozglue/misc/TimeStamp_darwin.cpp

@@ -136,8 +136,6 @@ void TimeStamp::Startup() {
     ;
 
   gInitialized = true;
-
-  return;
 }
 
 void TimeStamp::Shutdown() {}
@@ -146,6 +144,10 @@ TimeStamp TimeStamp::Now(bool aHighResolution) {
   return TimeStamp(ClockTime());
 }
 
+uint64_t TimeStamp::RawMachAbsoluteTimeNanoseconds() const {
+  return static_cast<uint64_t>(double(mValue) * sNsPerTick);
+}
+
 // Computes and returns the process uptime in microseconds.
 // Returns 0 if an error was encountered.
 uint64_t TimeStamp::ComputeProcessUptime() {

mozglue/misc/moz.build

@@ -110,14 +110,14 @@ if CONFIG["OS_ARCH"] == "WINNT":
             "PreXULSkeletonUI.cpp",
         ]
 
-elif CONFIG["HAVE_CLOCK_MONOTONIC"]:
-    SOURCES += [
-        "TimeStamp_posix.cpp",
-    ]
 elif CONFIG["OS_ARCH"] == "Darwin":
     SOURCES += [
         "TimeStamp_darwin.cpp",
     ]
+elif CONFIG["HAVE_CLOCK_MONOTONIC"]:
+    SOURCES += [
+        "TimeStamp_posix.cpp",
+    ]
 elif CONFIG["COMPILE_ENVIRONMENT"]:
     error("No TimeStamp implementation on this platform.  Build will not succeed")